This invention relates to improved coupling mechanisms for dielectric resonator loaded cavity filters.
It is well-known that TE01 resonant modes may be coupled to one another simply by placing two dielectric resonators in the same cavity. The closer the dielectric resonators are to one another, the stronger the coupling.
In order to control coupling between such adjacent resonators, an iris or window may be positioned between the two dielectric resonators. The degree of coupling may be adjusted by changing the dimensions of the window or iris.
To adjust the coupling between resonators using a window or iris, typically in the past the filter had to be disassembled so that the window or iris size could be changed. That requirement was eventually dispensed with, and a variety of mechanisms for tuning dielectric resonator loaded cavity filters were developed having coupling mechanisms that were easily tunable without the need for filter disassembly. These include the tuning mechanisms shown in U.S. Pat. No. 5,805,033. For example, in FIG. 1 of U.S. Pat. No. 5,805,033, tunability was provided by using a coupling screw extending from the side of the filter which was parallel to the electric fields of the resonators. Adjustment of the screw provided tunability but, of course, required side access for tuning which was sometimes virtually impossible to provide. In the embodiment of FIGS. 6 and 7, another tuning mechanism is shown. Although it is effective and advantageous, it does depend upon the experience and expertise of the tuner at the time of assembly.
In accordance with the present invention and in one form of the invention, an improved dielectric resonator loaded cavity filter assembly comprises a housing and a cover defining an interior surrounded by an exterior. The housing interior defines at least two adjacent cavities having respective dielectric resonators mounted therein. The adjacent cavities are separated by a transverse partition defining an iris or coupling window therein, the coupling window having two spaced opposing sidewalls confronting each other, each of the sidewalls defining an inwardly extending shoulder portion intermediate its length. A conducting coupling strip is removably secured and grounded to the shoulder portion of one sidewall, as by a fastening screw. The strip extends across the coupling window, substantially parallel to the cavity bottoms, and toward and over the shoulder portion of the other sidewall. The coupling strip is positioned above and over the shoulder portion of the second sidewall and defines a gap between the strip and the shoulder portion. The filter further comprises a tuning screw secured by threading to the housing, the tuning screw having an outer free end accessible from the exterior of the housing and cover, and an internal end disposed adjacent the coupling strip, whereby when the tuning screw is rotated relative to the housing, the internal end of the screw moves toward and away from the coupling strip in a direction perpendicular to the cover for tuning without requiring access to the coupling strip. Desirably, the sidewall shoulders are vertically offset from each other and the coupling strip is spaced away from the shoulder of the other sidewall. In a most preferred form, the coupling strip lies in a flat plane throughout its length. In a preferred form, the resonators are mounted to the cover and the tuning screw is secured to the base of the housing.
A further improved dielectric loaded cavity filter in accordance with this invention comprises a housing and a cover defining an exterior and an interior, the housing interior defining at least two adjacent cavities having respective dielectric resonators mounted therein, with the adjacent cavities being separated by a transverse partition defining a coupling window in the housing. The coupling window has two spaced opposing sidewalls confronting each other, one of the sidewalls defining an inwardly extending shoulder portion below which a relatively narrow window portion is provided and above which a relatively wide window portion is provided, the ratio of the relatively wide window portion to the relatively narrow window portion being at least 2.0 to 1. A tuning screw is secured by threading to the housing, the tuning screw having a tool engaging outer end accessible from the exterior of the housing and cover, and an internal portion and internal end extending parallel to the coupling window and being generally coplanar therewith, the coupling screw overlying the shoulder and lying closely adjacent to the edge, whereby when the tuning screw is rotated relative to the housing, the internal end of the screw moves toward or away from the shoulder in a direction perpendicular to the cover.